How do I lock my MBP screen without locking my keychain?

Solution 1:

If you have a screensaver you can lock that with your password so whenever screensaver tries to quit it needs a password. To set this up, first set up your screensaver if you don't have one. Then open System Preferences/Security and Privacy. Click the first tab in that window named General. The 2nd line on this box allows you to set a password associated with the screensaver.

Solution 2:

This is not possible since interactive keychain usage is limited to console authorization. When the screen is locked, all of that is revoked. On top of that, it’s not that you are locking the screen, but you are locking your session which includes not only the screen, but keychains, DMA, smartcards and some networking capabilities as well.